Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
1998-05-15
2002-06-25
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S107000, C522S136000
Reexamination Certificate
active
06410611
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an active energy ray curable composition comprising a maleimide derivative, which is useful for various coatings, inks for printings, surface finishes, moldings, laminated plates, adhesives, and binders. More specifically, the present invention relates to an active energy ray curable composition comprising a maleimide derivative which can be cured in the absence of a photoinitiator under irradiation of ultraviolet light with practical intensity and energy value of irradiating light, and a method for curing the said curable composition.
BACKGROUND ART
An active energy ray curable composition polymerized under irradiation of active energy rays such as ultraviolet light, visible light, and the like, has an advantage of being rapidly cured. Therefore, active energy ray curable compositions are widely used as paints, inks for printing, adhesives, coatings, and the like. However, conventional active energy ray curable compositions cannot initiate polymerization alone upon irradiation of an active energy ray; therefore, it is necessary to use a photoinitiator together therewith. When a photoinitiator is used in large quantities, curing rapidly progresses. Therefore, large quantities of a photoinitiator tend to be used.
As photoinitiators, compounds having an aromatic ring, are used in general because they effectively absorb ultraviolet light. The photoinitiators have problems such as yellowing of cured materials upon addition of heat or light. Moreover, compounds of low molecular weight are commonly used as photoinitiators because solubility of a photoinitiator to active energy ray curable monomers and/or oligomers is necessary to initiate photopolymerization effectively. A photoinitiator having low molecular weight has high vapor pressure; therefore, many photoinitiators tend to give off unpleasant odors at room temperature to 150° C. Because infrared light in addition to ultraviolet light is generated from an ultraviolet light lamp, one of the light sources of active energy rays, active energy ray curable compositions are substantially heated upon irradiation with many ultraviolet light lamps arranged side by side. Therefore, unpleasant odors are given off from photoinitiators, and as a result, the working environment becomes worse.
Unreacted or decomposed photoinitiators remain in the cured compositions after irradiation of active energy ray curable compositions containing photoinitiators with active energy rays; therefore, problems are caused such as changing the color thereof to yellow, giving off unpleasant odors, and the like, when the cured compositions are exposed to light or heat. In particular, when a material at high temperature, such as a thermal head, contacts the active energy ray curable composition comprising a photoinitiator, strong unpleasant odor is given off. Moreover, when the cured composition after irradiation of an active energy ray curable composition containing a photoinitiator is contacted by water, unreacted photoinitiator is exuded; therefore, it is unsuitable to use the active energy ray curable composition as wrapping for food.
In order to solve these problems, a curable resin comprising a polymer with polymerizable unsaturated acrylic group and an organic solvent-soluble styrene containing an acrylic thermoplastic resin are disclosed in JP-A-58-89609 (the terms “JP-A-58-89609” as used herein mean “unexamined published Japanese patent applications”) as an active energy ray curable composition without a photoinitiator. Photopolymerizable adhesive compositions comprising a copolymer of methacrylate monomer and/or methyl acrylate and a photopolymerizable monomer are disclosed in World Patent No. 89-05827.
Moreover, a photopolymerizing method in which maleimide compound is used as an electron acceptor for a charge-transfer complex which is formed by the electron acceptor and an electron donor, is disclosed in U.S. Pat. No. 5,446,073 and
Polymer Preprints,
vol. 37, No.2, pp. 348-349, 1996.
In addition, it was reported that the maleimide derivatives can polymerized in the absence of photoinitiators under irradiation of UV light in
Polymer Letters,
vol. 6, pp. 883-888, 1968. The active energy ray curable compositions comprising maleimide derivatives are disclosed in JP-A-61-250064, JP-A-62-64813, and JP-A-62-79243. The alkylmaleimides and arylmaleimides are used in these well-known documents, however, the maleimide derivatives in the documents show low photoinitiator properties; therefore it is necessary to use substantial amounts of a photoinitiator together with the maleimides.
It is well-known that pendant type maleimides can be crosslinkable by UV irradiation ([2+2]-photocycloaddition reaction). For example, photopolymerizable polymers having an &agr;-aryl substituted maleimide group at a side chain are disclosed in U.S. Pat. No. 3,920,618, JP-A-50-123138, and JP-A-51-47940. The polymers having side chain type maleimide group having an alkyl substituent are disclosed in U.S. Pat. No. 4,079,041 and Europe Pat. No. 21019. These pendant type maleimides cannot be used in formation of liner polymers by photopolymerization; therefore, they are commonly used to prepare a negative printing plate. Moreover, these pendant type maleimides have some problems that a photocross-linking dimerization reaction needs rather long time (several tens seconds to several minutes) with an excess amount of irradiation energy.
In addition, photocurable compositions comprising maleimide derivatives as electron acceptors and vinyl ethers as electron donors are reported in
Polymer Materials Science and Engineering,
vol. 72, pp. 470-472, 1995 and
Proceedings of RadTech Europe
95, pp. 34-56, 1995. The photopolymerizable compositions comprising 1,4-bis(vinyloxymethyl)cyclohexane and N-cyclohexylmaleimide or the photopolymerizable compositions comprising 4-hydroxybutyl vinyl ether and N-(hydroxyalkyl)maleimide are disclosed in these documents. They are polymerized upon UV-irradiation in the absence of a photoinitiator, however, hardening of the coated films cannot occur; i.e. the coated films maintain liquid states after UV-irradiation.
Maleimides such as N,N′-4,9-dioxa-1,12-bismaleimidedodecane are disclosed in
Polymer Preprints,
vol.37, No. 2, pp. 348-349, 1996 as a photoinitiator for polymerization of 1,6-hexanediol diacrylate and polyethylene glycol 400 diacrylate. However, there are serious problems that many of these maleimides are solid and are hardly dissolved in acrylates.
The photocurable compositions disclosed in JP-A-58-89609 and World Pat. No. 89-05827 have a problem that they cannot be sufficiently cross-linked by a practical irradiation energy.
Moreover, the polymerizing methods disclosed in U.S. Pat. No. 5,446,073 and
Polymer Preprints,
vol. 37, No. 2, pp. 348-349, 1996 have a problem in that high irradiation intensity is necessary to cure sufficiently. Many maleimide derivatives disclosed in the documents are solid at ambient temperature, and moreover, it does not suggest whether the maleimide compounds are homo-polymerized upon irradiation of UV-light in the absence of a photoinitiator in the documents. The documents disclose that specified maleimide derivatives react with vinyl ethers and acrylates in the absence of photoinitiators. However, it is difficult to obtain cured coatings with practical properties by the polymerization method disclosed in the former. From the view points of solubility to unsaturated compounds, it is also difficult to obtain cured coatings in wide range of the compositions by the polymerization method disclosed in the latter.
In addition, the maleimide derivatives disclosed in
Polymer Letters,
vol. 6, pp. 883-888, 1968 are solid at ambient temperature, and it is impossible to obtain the cured coating with practical properties by polymerization of the maleimide derivatives in solid state.
The polymers having a maleimide group as a side chain disclosed in U.S. Pat. No. 3,920,618, JP-A-50-123138, JP-A-51-47940, U.S. Pat. No.4,079,041, and Europe Pat.
Ishikawa Hidenobu
Miyakawa Atsushi
Sakurai Yoshinobu
Takahashi Katsuji
Yonehara Hisatomo
Dainippon Ink and Chemicals Inc.
Mullis Jeffrey
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